From 11b4746127bf864df869975d028f2afdbb66d044 Mon Sep 17 00:00:00 2001
From: Sam Calisch <sam.calisch@cba.mit.edu>
Date: Wed, 21 Feb 2018 14:53:56 -0500
Subject: [PATCH] Update README.md

---
 printed-stepper/README.md | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/printed-stepper/README.md b/printed-stepper/README.md
index 9bf957e..2d1399b 100644
--- a/printed-stepper/README.md
+++ b/printed-stepper/README.md
@@ -1,3 +1,9 @@
+## Printed stepper motor
 
+The motor below was printed using <a href='https://www.proto-pasta.com/pages/magnetic-iron-pla'>Proto Pasta's Iron-doped PLA</a>, which has a relative permeability of around 10.
 
-<img src='printed-stepper.jpg' width=300px>
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+<img src='printed-stepper.jpg' width=600px>
+
+This directory contains STLs and a Fusion design file.
+
+Be warned -- there are a few crucial design errors!  First, the tooth size is too small given the reduced relative permeability of this filament, as compared to magnetic steel ($`\mu_r \approx 1000`$).  Second, while the two magnetic poles have a full tooth offset, the two electrical phases don't have a half tooth offset.  Duh!  So, even if the tooth size we correct, the stepper wouldn't step in a predicatble direction.  Someday I'll fix these and print another...
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-- 
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